Burst containment means

ABSTRACT

The invention relates to a means for containing burst fragments generated when very high speed machinery, particularly gas turbines, rupture. The containment means is a winding of tape over the machinery housing and radially aligned along the expected path of travel of part fragments. The winding is formed from lightweight material having high strength and high elongation properties providing unusual energy absorbing capabilities which tends to contain the impact of burst fragments primarily by deflection rather than high yield stresses.

United States Patent 3,203,180 8/1965 Price Inventor Salvatore MottaLowell, Mass.

App]. No. 825,724

Filed May 19, 1969 Patented Aug. 31,1971

Assignee Avco Corporation Cincinnati, Ohio BURST CONTAINMENT MEANS 2Claims, 4 Drawing Figs.

U.S. C1 41-5/9, 74/608.415/197,415/214 Int. Cl Fl6p 1/02 Field of Search74/608,

References Cited UNITED STATES PATENTS 1,698,514 1/1929 Schmidt 74/6092,848,133 8/1958 Ramberg..... 156/189 2.999.667 9/1961 Morley 230/1323,272,672 9/1966 Lampman et a1. 156/189 FOREIGN PATENTS 1.013.09612/1965 Great Britain 415/174 Primary Examiner- Henry F. RaduazoAuorneys-Charles' M. Hoganand and Abraham Ogman ABSTRACT: The inventionrelates to a means for containing burst fragments generated when veryhigh speed machinery, particularly gas turbines, rupture. Thecontainment means is a winding of tape over the machinery housing andradially aligned along the expected path of travel of part fragments.The winding is formed from lightweight material having high strength andhigh elongation properties providing unusual energy absorbingcapabilities which tends to contain the impact of burst fragmentsprimarily by deflection rather than high yield stresses PATENIED was]l97| 3602.602

I N VENTOR. SALVATORE MOTTA BY M A ORNEY BURST CONTAINMENT MEANS Thecontainment means described is used for the purpose of containing burstfragments within a localized area in the event the rotor of a very highspeed machine ruptures. The invention has immediate application to thecompressor section of gas turbines and can be further extended to theturbine section following the development of a high temperature and highelongation plastic fiber such as ahigh temperature nylon known as N orelfor example.

In the past a metal, usually steel, in a single mass, laminated or wovenform has been used. In one respect steel would appear to be an excellentcandidate. in practice, particularly in aviation gas turbineapplications, it is practically useless for a rather unusual reason, tobe demonstrated.

It is an object of the invention to provide a burst containment meansfor high energy fragments which (i) avoids the limitations anddisadvantages of prior art devices, (ii) is lightweight and compact,(iii) made from material which is capable of absorbing at least twice asmuch kinetic energy as steel of the same weight, (iv) is constructedfrom a nylon tape material having a high strength to failure ratio, and(v) comprises a winding of at least turns of tape.

in accordance with the invention a burst containment means comprises ahousing, a winding made up of at least 15 overlying turns of a tapeformed from a material having a specific energy absorbing capability ofat least 200,000 (lN-LB/LB).

The novel features that are considered characteristic of the inventionare set forth in the appended claims; the invention itself, however,both as to its organization and method of operation, together withadditional objects and advantages thereof, will best be understood fromthe followingdescription of a specific embodiment when read inconjunction with the accompanying drawings, in which:

FIG. 1 is a partial cross-sectional representation of a burstcontainment means embodying the principles of the present invention;

FIG. 2 is a schematic representation of the winding comprising a portionof the burst containment means;

FlG. 3 is an expanded segmented view of the burst containment meansshowing structural details; and

FIG. 4 is a pictorial representation of the invention in the act ofrestraining high kinetic energy fragments.

The energy absorbing capability ofa material is determined by referenceto a standard stress-strain curve of the material where stress isspecified in LB/lN and the strain in lN/lN. The energy absorbingcapability ofa material is determined by calculating the area under thestress-strain curve.

in tests conducted on a nylon ballistic cloth material the energyabsorbing capability of the material was determined to be 8,000(lN-LB/lN). The energy absorbing capability of steel that was consideredsuitable for fragment containment was determined to be 35,000 (lN-LB/lNit would appear from the foregoing that steel is much more suited forfragment containment than the nylon cloth. The fact of the matter is,however, that it is, from a practical point of view, much worse. For onething, steel, because it has a high modulus of elasticity, tends toresist an impact with negligible deflection and consequently it tends toshatter rather than absorb energy.

Another very serious limitation of steel is its weight. For example, thespecific energy absorbing capability, ie the energy that a material canabsorb per pound of material, of steel is 121,000 (lN-LB/LB.) Thespecific energy absorbing capability of nylon, on the other hand, is204,000 (IN-LB/LB) and is in fact a preferred candidate material.

The low strength material is utilized to its fullest capability when itis wound into a coil or winding containing at least 15 turns for reasonsthat will be explained hereinafter.

Referring to FlG. 1 of the drawings there is illustrated ing crosssection the pertinent elements of a gas turbine compressor assembly 10.The assembly includes a hub 11 on the circumference of which arefastened a plurality of compressor blades 12. Surrounding and spacedfrom the compressor blades 12 is a housing 13 formed from any suitablemetal material.

Lapped around the housing 13 is a winding 14 comprising at least 15turns 16.

The turns 16 are formed from a continuous length of a material having aspecific energy absorbing capability of 200,000 (lN-LB/LB) or greater. Anylon ballistic cloth as defined and identified in the Mill Standardspecification Mil-(3123690 is the preferred material to use in making upthe winding of 14.

FIG. 2 is a schematic representation showing the use of a continuoustape in making up the winding 14. It also represents schematically thatthere are no means for bonding or fastening the adjacent turns 16 of thewinding 14 to each other or to the housing 13.

HO. 3 is another representation of the winding structure providingadditional detail.

FIG. 4 of the drawings serves to illustrate why it is important to 1)provide a plurality of turns 16 preferably a minimum of 15 turns, and(2) provide a winding where adjacent turns are free to move relative toeach other. FIG. 4 illustrates the winding 14 in the process ofabsorbing three high energy fragments from an exploding mechanicalmember. The housing 11 has been completely shattered and is no longer afactor in containing the fragments. The configuration of the winding 14has changed into an optimum configuration for the type of impact it isresisting. The wide center portion 19 of the three legs of the windingindicate that'a number of turns 16 of the winding 14 have failed intension. The high density of turns 16 adjacent to the outside of thewinding 14 indicate that a substantial number of turns 16 are compressedand absorbing the energy applied to the winding by the fragments.

it is clear that the amount of energy that is to be contained will varywith the speed and the configuration of the high energy fragments. Theprimary use of the housing relates to its function in connection withthe gas turbine compressor. Its very presence causes it to absorb someof the energy from fragments; but because it is made of metal andbecause its thickness is determined by the gas turbine performance, itis not a' good energy absorber and in fact the major portion of theenergy contained in a fragment is absorbed by the winding 14. Onoccasion it has been noted that the housing upon rupturing createssecondary high energy fragments but generally these do not pose aserious problem.

A number of tests have been made by preparing a 3-inch wide winding overan 18-inch diameter housing. Each turn was one thirty-second inch thickand 33% turns were used to make up the complete winding. This particulardesign has successfully resisted impact up to and including 83,500IN-lbs. Up to 40 percent of the turns experienced one or more breaks.These breaks were examined and were determined to be tension breaks. Theintact" turns underwent appreciable elon' gation. High energy fragmentswere completely contained in the windings.

The various features and advantages of the invention are thought to beclear from the foregoing description. Various other features andadvantages not specifically enumerated will undoubtedly occur to thoseversed in the art, as likewise will many variations and modifications ofthe preferred embodiment illustrated, all of which may be achievedwithout departing from the spirit and scope of the invention as definedby the following claims:

1. A burst containment means comprising the combination of a housingabout a rotated bladed structure, a winding on said housing consistingessentially of at least 15 overlapping turns of a tape formed from anylon ballistic material having a specific energy absorbing capabilityof at least 200,000 (lN-LB/LB).

2. A burst containment means as defined in claim 1 in which the windingis formed from a woven tape of a nylon ballistic material.

1. A burst containment means comprising the combination of a housingabout a rotated bladed structure, a winding on said housing consistingessentially of at least 15 overlapping turns of a tape formed from anylon ballistic material having a specific energy absorbing capabilityof at least 200,000 (INLB/LB).
 2. A burst containment means as definedin claim 1 in which the winding is formed from a woven tape of a nylonballistic material.